Parabolic Drill Bits (Nathan?)

Rudy Joly

Well-Known Member
What are parabolic bits used for specificly ?
I remember using one a few years ago, the thing spun the drill in my hand when it grabbed. That was just a 1/4" bit. I keep seeing them in the tool catalogs and I just have to know what they're made for.
Thanks
 
I'm a little embarrassed to admit, but I don't really know much about parabolic drill flute grind design. I know I use them when machining plastic and aluminum because the drill types recommend for those applications frequently have the parabolic flute grinds. Many of the "high performance" drills that are designed for large chip loads and reduced pecking utilize a not-so-vanilla flute grind.

I believe the "standard" drill bit flute grind is basically an O grind with some ground relief behind the flute to reduce rubbing. I expect the parabolic grind shape does a couple things - it may allow more aggressive edge geometry at the intersection of the flute and the lip, and opens the flute to allow more room for chips to get out and coolant to get in. It may also enhance chip ejection. It is my impression they also tend to cause fewer burrs at the internal intersection of holes.

I regularly drill 1/2" diameter holes 2" deep in solid PVC plastic in a single peck at 80 IPM. On retraction, the "chip" flies off the bit and hits the inside of the machining enclosure with a nice "wack". Folks who haven't seen the program run before wince at first when they see it. It doesn't wrap around the cutter into a birds nest or melt into a PVCsicle . This is a cobalt HSS parabolic bit. I'm not really sure about how the flute technology affects this, but I do know a "standard" doesn't work well when pressed like this.

I wish I could answer your question better - but I don't really know.

I'm not surprised it grabbed on you - I believe they tend to have fairly aggressive geometry. I think they're generally used in deep holes where you don't want to have to peck a lot.
 
parabolic-style drills/heavy-web drills offer higher rigidity and increased flute area for chip removal on deep-hole drilling operations and typically use a split point cutting edge.


Travis
 
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